1. Field of the Invention
The present invention relates to the treatment of dermatologic scars, and more particularly concerns scar treatment sheeting and other articles, and a method of manufacture thereof.
2. Description of the Prior Art
Silicone chemistry has evolved since the early 1900's into a wide variety of systems used for industrial as well as medical applications. Medical grade silicones are usually based on thermoset dimethyl systems, whereby the molecular formula may be represented as follows: ##STR1##
A crosslinking agent is used to create bonds between the hydrogen atoms on the methyl groups of adjacent molecules. These silicone formulations are often supplied as a two(2) part system, wherein one part contains a catalyst for vulcanization and the other part contains the base resin and crosslinking agent. By varying the amount of crosslinking agent, the crosslink density may be adjusted to achieve desired bulk or surface qualities of the vulcanized elastomer. Physical strength and durability tend to increase, while softness and coefficient of friction decrease with higher crosslink densities. Materials with a high crosslink density are relatively slick and tough, but have poor compliancy or "drapability". Silicones with low crosslink densities give a soft gel with a more adhesive or "tacky" surface. These materials are more drapable, although they are inherently weak and tend to fragment easily with low levels of stress.
A number of U.S. Patents and other publications relate to the field of the invention, and are as follows:
U.S. PATENT DOCUMENTS
______________________________________ 4,832,009 5/23/89 Dillon 4,945,125 7/31/90 Dillon et al. 5,066,683 11/19/91 Dillon et al. 5,157,058 10/20/92 Dillon et al. ______________________________________
OTHER PUBLICATIONS
Sperling, Interpenetrating Polymer Networks and Related Materials, Plenum Press, New York, 1981, pp. 1-5.
Dillon, ME, Okunski, WJ, "Silon.RTM. Non-Adherent Film Dressings on Autograft and Donor Sites", Wounds, 1992, vol. 4, no. 5:203-207.
Dillon, ME, "Silicone and Poly(tetrafluoroethylene) Interpenetrating Polymer Networks: Brief History, Summary of Recent Developments, and Discussion of Applications", Interpenetrating Polymer Networks, Klempner et al. ed, ACS Books, New York, N.Y., 1991, pp. 393-404.
Perkins, et. al., "Silicone Gel: A New Treatment for Burn Scars and Contractures", Burns, 1982, 9, pp. 201.
Quinn, KJ, "Silicone Gel in Scar Treatment", Burns, 1987, 13, pp. 33-40.
This invention relates to the treatment of dermatologic scars associated with traumatic or surgical injuries by using silicone elastomer materials. In many cases, scar formation may be excessive, resulting in raised, textured or colored surfaces. Scars can not only be disfiguring, but also limit range of motion and functionality. Historically, the application of pressure to an affected area of the body has been used to minimize these effects, particularly regarding hypertrophic and keloidal scars. Garments made of an elastic textile are used to achieve such pressure. This method of treatment eventually became a standard of care in many medical institutions, particularly burn treatment centers.
An Australian research group reported using silicone gel under pressure garments to evenly apply pressure in anatomic depressions, over areas of flexure, and during ambulation (Perkins et al., 1982). Quinn (1987) later found that the efficacy of silicone for scar modification was unrelated to pressure, in that the silicone material itself had a beneficial effect on the cosmetic appearance and elasticity of scars. The exact biological mechanism of this effect is not well understood.
In recent years, two(2) general types of silicone sheeting products have gained commercial acceptance in the marketplace for scar modification applications. One of the first types, Silastic.RTM. (Dow Corning Corporation) consists of a soft polydimethylsiloxane ("PDMS") gel material of approximately 0.125 inch (0.32 cm) in thickness. The low modulus of elasticity is beneficial by providing surface tack, thus promoting skin contact on difficult anatomical areas or during movement. The PDMS composition is inherently weak, however, and endures only several days in practice before breaking apart because of mechanical agitation. The above mentioned product uses a reinforcing scrim embedded into the body of the material to improve durability. This macroscopic mesh complicates the manufacturing process and may cause skin irritation if exposed during use. Although durability is increased, these products still disintegrate from normal wear and tear within a matter of weeks. This is a limiting factor in the cost effectiveness of the product in that the treatment may last for several months, thus requiring numerous repurchases. Together, the scrim and thickness of the product compromise drapability and comfort features.
The second type of commercial product, such as Sil-K.RTM. (Degania Silicone, Ltd.), consists of a relatively stiff silicone elastomer of approximately 0.03 inches (0.08 cm) in thickness. The increased modulus of elasticity provides for increased physical strength and durability, and the lack of a reinforcing scrim simplifies the manufacturing process. The material is relatively non-adherent, so adhesive tape is typically used to maintain the position of the material on the body. Although this material may last for the duration of treatment, it does not conform well to anatomical areas and does not provide a high level of patient comfort. This compromises patient compliancy and may limit the efficacy of the treatment.
Both types of products are relatively occlusive and impermeable to moisture vapor, which further detracts from patient comfort. There are other silicone-based scar treatment materials which have been commercialized, each generally falling into one of the two categories above. Some of the important properties of the above two examples of commercial products are listed in Table VII.
Definitions
Moisture Vapor Transmission Rate
The rate at which water vapor permeates through a material calculated gravimetrically and expressed in units of g/m.sup.2 /day. The test conditions are 50% relative humidity, 98.degree. F. (37.degree. C.), with an air flow of 650 cubic feet per minute over the specimen.
Tensile Strength
The load required to break a test specimen divided by the cross-sectional area of the specimen.
Modulus of Elasticity
The tensile strength of a material at break divided by the elongation at break.
Coefficient of Friction
The force, measured in pounds, required to initiate the slide of a 1 inch square (6.45 cm.sup.2) by 0.5 inch (1.27 cm) thick piece of high density polyethylene over a test specimen on a horizontal surface.
Drapability
The distance the edge of a length of material bends when extended one inch beyond the surface of a ridged support with a corner radius of less than 1/16th inch.